One Saturday, Ann got up early and ran twenty miles. She relaxed over breakfast, then headed back out for twenty more. She had some plumbing chores around the house, so after finishing run No. 2, she hauled out her toolbox and got to work. By the end of the day, she was pretty pleased with herself; she’d run forty miles and taken care of a messy job on her own. So as a reward, she treated herself to another fifteen miles.